Organic Geochemical Characteristics of the Upper Cretaceous Qingshankou Formation Oil Shales in the Fuyu Oilfield, Songliao Basin, China: Implications for Oil-Generation Potential and Depositional Environment

Round 1

Reviewer 1 Report

The manuscript under consideration presents some geochemical data on organic-rich rocks of the central Songliao Basin. The data may be interesting, especially for the local petroleum exploration. However, their presentation and geological interpretation are poor. The paper language needs severe editing. Its organization should also be carefully revised, because of significant mixing between results and discussion. The text contains a lot of mistakes. Even in the title, the studied Qingshankou Formation is indicated as Lower Cretaceous that does not correspond to the text below. Introduction and Discussion are not complete. Conclusions are not solid and repeat those from the previous studies, including the fallacious ones.

Some significant previous works are not considered adequately or at all. For example, Hou et al. (2000) and Wan et al. (2013) presented some data on organic geochemistry and Corg. isotopic records of Qingshankou Fm., respectively. They should be mentioned in the Introduction section and discussed in the corresponding parts of the text.

The paper does not pay respect to the most recent chronostratigraphic and geochemical data on the matter. In particular, the Qingshankou Formation (92-86 Ma; Scott et al., 2012; Xi et al., 2012; Wang et al., 2019) and underlying Quantou Formation is dated as Turonian-Coniacian. So, deposition of the studied oil shale may not be correlated with OAE2 (Cenomanian/Turonian boundary, 94 Ma), that almost completely destroys the authors’ interpretation.

REFERENCES

Wang, C. et al., 2019. Initial report of continental scientific drilling project of the Cretaceous Songliao Basin (SK-1) in China. Amsterdam, The Netherlands; Cambridge, MA : Elsevier, 695 pages.

Ноu, D., Li, M., Huang, Q., 2000. Marine transgressional events in the gigantic freshwater lake Songliao: paleontological and geochemical evidence. Organic Geochemistry 31, 763-768.

Author Response

Dear reviewer

I'm glad to receive your suggestions and comments . These suggestions are highly scientific and professional, and detailed, which will definitely help to improve the quality of papers. After studying your comments carefully, I made in-depth thinking to analyze the problems and solve them under your guidance. Here is my point-by-point response to the your comments . Thank you very much for your guidance, if there are still deficiencies and need to be corrected,please let me know! Thank you again!

Please see the attachment.

Best regards,

Wentong He

Author Response File: Author Response.doc

Reviewer 2 Report

Dear Editor,

The authors did a gorgeous work on understanding the oil-generation potential and the depositional environment of the

Qingshankou Formation oil shale using geochemical data from various methods of analyses. New scientific knowledge is coming from this significant effort that is also very useful to the E&P industry. However, I cannot propose the acceptance of the MS at present form since significant changes should be made.

I attach you an annotated pdf file of the MS with my remarks. Following are also some very important issues that in my view have to be addressed:

Language mprovement. In many cases the data that are presented are truly important but the language does not support them at all. Please pay high attention to this issue. I would definitely suggest to separate the results from the discussion. This will significantly improve the level of the manuscript and most importantly the reader can follow the reasoning behind the interpretation of the resulted data. At its present form I had many problems to understand what is interpretation and what is data. Panctuation is really bad. Please check in details. Check also the reference list to be consistent with the jurnal's instructions.

I look forward seeing this manuscript published.

Comments for author File: Comments.pdf

Author Response

Dear reviewer

I'm glad to receive your suggestions and comments . These suggestions are highly scientific and professional, and detailed, which will definitely help to improve the quality of papers. After studying your comments carefully, I made in-depth thinking to analyze the problems and solve them under your guidance. Here is my point-by-point response to the your comments . Thank you very much for your guidance, if there are still deficiencies and need to be corrected,please let me know! Thank you again!

Please see the attachment.

Best regards,

Wentong He

Author Response File: Author Response.doc

Reviewer 3 Report

​Dear Authors,

The topic is so interesting but I believe this article was written in a hurry and not reviewed. First you have to do that and see if the paragraphs are flowing though making sense to each other and overall building a story that you want to tell. As a reader I was lost and the main reason is because the facts were piled in the article without c​​onsidering its continuity.

Also, I believe you did a terrible job with your punctuation, your formatting (paragraph as well as chemical formula) and overall sentence construction. I strongly believe, before you submit this paper again in future please have consultation with someone with ​the ​English language background.

Currently I am uploading a marked and commented PDF for you to work on. Many of the comments point out a generic mistake at one or few places, which you need to check in the entire document. I have not identified and marked the same mistake everywhere in your article. That's your job.

With all that being said, I am recommending this article to undergo major revision along with English check before being considered to be reviewed again.

Thanking you,

With best regards,

Comments for author File: Comments.pdf

Author Response

Dear reviewer

I'm glad to receive your suggestions and comments . These suggestions are highly scientific and professional, and detailed, which will definitely help to improve the quality of papers. After studying your comments carefully, I made in-depth thinking to analyze the problems and solve them under your guidance. Here is my point-by-point response to the your comments . Thank you very much for your guidance, if there are still deficiencies and need to be corrected,please let me know! Thank you again!

Please see the attachment.

Best regards,

Wentong He

Author Response File: Author Response.doc

Round 2

Reviewer 1 Report

First of all, I do not have time to carefully review the revised manuscript currently. So I just checked how the authors corrected the text after my comments. The following has been found.

The main question of how OAE2 corresponds to the bio-geochemical fluctuations revealed in the studied Qingshankou Formation is still unclear from this study. As far I can understand, the authors currently suggest that the former are consequences of the latter, but somehow occurred 2 million years after OAE2 on the background of gradual decrease of pCO₂ in atmosphere. However, what does "During the OEA2 period, a large number of organic-rich oil shales of the Qingshankou Formation were deposited in lakes of the Songliao Basin" mean in Abstract? In addition, Fig. 2 shows that the studied oil shale is characterized by the negative d¹³C and positive TOC and TOC/TS excursions relative to both underlying siltstone and overlying mudstone. Thus, these records indicate some "sharp" event rather than a gradual evolution.

A discussion is almost absent in the manuscript. Results of the previous studies are just mentioned, not critically discussed. Some significant previous works are not mentioned at all. For example, Wan et al. (2005; Sorry, I mistakenly referenced Wan et al. (2013) in my previous review) and Jones et al. (2018), that presented the d¹³C_org, TOC and TOS records and other geochemical data for the studied Qingshankou Formation, are not even mentioned.

So the manuscript should be either seriously revised again or rejected, although the data as themselves may be worth of publication.

References

Wan, X., Li, G., P. Chen, Yu, T., Ye, D., 2005. Isotope Stratigraphy of the Cretaceous Qingshankou Formation in Songliao Basin and its correlation with marine Cenomanian Stage. Acta Geologica Sinica, 2 available at http://en.cnki.com.cn/Article_en/CJFDTOTAL-DZXE200502001.htm.

Jones, M.M., Ibarra, D.E., Gao, Y., Sageman, B.B., Selby, D., Chamberlain, C.P., Graham, S.A., 2018. Evaluating Late Cretaceous OAEs and the influence of marine incursions on organic carbon burial in an expansive East Asian paleo-lake. Earth and Planetary Science Letters, 484, 41-52.

Author Response

Dear reviewer

Thank you for recommending these two excellent articles to me. These papers have good scientific research value. In these papers, the samples of SK-1 well are be used to conduct a fine study of the stratigraphic geochemical changes of the whole Qingshankou formation, providing excellent data for the study and comparison of other areas in Songliao basin.

I read and quoted these articles carefully, got great inspiration, and overhauled my manuscript. There are two main problems.

I have revised the reason for the the negative δ¹³C_orgdeviation in the Qingshankou formation. Theglobal carbon cycle, warm-humid palaeoclimate and dynamic local biogeochemical cycling were the most likely reasons for the TOC increase and negative δ¹³C_org deviation. In this paper, we compare δ¹³C_org, TOC and TS records and other geoscience data with previous studies, modify some explanations, and find that these records show that the negative δ¹³C_organd positive TOC of Qingshankou formation is a special "sharp" event, rather than a grand evolution of the whole Turonian period.

And I edited the modified Manuscript by English editing service. Thank you very much for your guidance, if there are still deficiencies and need to be corrected,please let me know! Thank you again!

Please see the attachment.

Best regards,

Wentong He

Author Response File: Author Response.doc

Reviewer 2 Report

Dear editor,

I would like to suggest a minor change. In line 234 of the MS, please change the word "higher" with the word "elevated". Otherwise there is no meaning in the sentence.

I look forward seeing this very interesting MS published.

Author Response

Dear reviewer

I'm glad to receive your suggestions and comments.  Thank you very much for your guidance, if there are still deficiencies and need to be corrected,please let me know! Thank you again!

Please see the attachment.

Best regards,

Wentong He

Author Response File: Author Response.doc

Reviewer 3 Report

Dear Authors,

I appreciate the changes and happy to read the article now.

Thanks for the work.

Best,

Author Response

Dear reviewer

I'm glad to receive your suggestions and comments.  Thank you very much for your guidance, if there are still deficiencies and need to be corrected,please let me know! Thank you again!

Please see the attachment.

Best regards,

Wentong He

Round 3

Reviewer 1 Report

The authors have corrected the manuscript after my comments. Thanks. However, the text still look fresh, including many unclearly written parts. I tried to improve some phrases (see the attached MS Word file), but it seems not enough. A serious editorial work is needed.

The discussion has been extended, but not very deepened. It is still uncertain, what was a main cause of the sharp negative d13C and positive TOC and TOC/TS signals near the base of Qingshankou Formation. Perhaps the authors should pay more attention to the tectonic history of the Songliao Basin including episodes of thermal subsidence and sea transgression on the background of relatively passive tectonism and warm-wet climate with some residual (after OAE2) greenhouse conditions. Note that they occurred just in the middle of post-rift stage of the Songliao Basin evolution (Fig. 12, Feng et al., 2010). These conditions could result in a unique (for the Songliao Basin) combination of slow sedimentation in a moderately salted, stagnant lake and abundant vegetation in the surrounding land that may explain the anomalous records obtained in this study. The authors’ current ideas are close to this understanding, are they?

Thus, I recommend a minor authors’ revision with a major editorial improvement for the current manuscript. Sorry for this uncertain conclusion.

Comments for author File: Comments.doc

Author Response

Dear reviewer

Thank you very much for your guidance. I carefully revised the manuscript according to your suggestion. Your suggestion is really professional and careful, which greatly improves the scientific level of my article. It's my lucky to meet you!!! If there are still deficiencies and need to be corrected,please let me know! Thank you again!

Please see the attachment.

Best regards,

Wentong He

Author Response File: Author Response.doc